Graphene reinforced concrete

ABSTRACT

A reinforced concrete material is described comprising a cementitious material (22) in which graphene is substantially uniformly distributed. A method of production of concrete is also described comprising the steps of forming a substantially uniform suspension (20) of graphene with water, and mixing the suspension (20) with a cementitious material (22) to form a concrete material (28).

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to concrete, and in particular to concretereinforced by the inclusion of a quantity of graphene therein, and to amethod of manufacture thereof.

2. Description of Related Art

Concrete is used as a building material in a very wide range ofapplications, including in the construction of buildings, bridges,pipes, paving materials and the like. In a number of applications, itsphysical properties have traditionally been enhanced by including in theconcrete reinforcing members such as steel reinforcing rods. Whilst suchmacro-scale reinforcements do successfully enhance, for example, theload bearing capacity of the concrete material, it has been found thatcorrosion of the reinforcing members can result in damage to thestructure manufactured using the concrete, limiting the life span of thestructure.

Other, nano-scale, reinforcing techniques are known, for example theinclusion of a range of additives to the concrete material can enhancethe chemical and/or mechanical bond between component parts of theconcrete material, enhancing its strength. During production ofconcrete, the cement particles thereof undergo a transformation from apower form to a fibrous crystal form upon reaction with water, and it isthe resulting mechanical interlocking of the crystals with one anotherand other components parts of the concrete that are responsible forgiving the concrete a significant part of its strength. The addition ofadditives such as carbon nanotubes and graphene oxide to the concretecan enhance the structure of the concrete, and so enhance its physicalproperties.

WO2013/096990 describes the incorporation of graphene oxide withincement and concrete for reinforcement purposes. One problem that isfaced in incorporating graphene oxide within cement and concrete is howto go about achieving a substantially uniform dispersion of the grapheneoxide within the cement or concrete material. In WO2013/096990, a methodis described that involves dispersing the graphene oxide within theliquid component of the cement or concrete before mixing the dispersionwith cementitious material to form the cement or concrete. However,graphene oxide is sufficiently hydrophilic that it tends to absorb asignificant part of the water contained within the concrete or cement,hampering hydration of the cement. As a consequence, the above-describedreaction is interfered with, and this can negatively impact upon theformation of the concrete. The incorporation of graphene oxide in thismanner to enhance the characteristics of concrete at an industrial scaleis thus not thought to be viable.

SUMMARY OF THE INVENTION

Bearing in mind the problems and deficiencies of the prior art, it istherefore an object of the present invention to provide concrete, and amethod of manufacture thereof, in which at least some of thedisadvantages associated with previously known materials and theassociated methods of manufacture are overcome or are of reduced impact.

It is another object of the present invention to provide a reinforcedconcrete material comprising a cementitious material in which grapheneis substantially uniformly distributed.

It has been found that the incorporation of graphene within concrete candramatically enhance certain properties of the concrete, theimprovements or enhancements being significantly better than arepossible by the incorporation of graphene oxide therein.

The graphene is preferably in the form of flakes. The flakes arepreferably of lateral dimensions of less than 5 μm, and more preferablyhave lateral dimensions in the range of 1-3 μm. More preferably, theflakes have a lateral dimension in the range of 1.5-2.5 μm, the flakespreferably having a lateral dimension in the region of 2 μm. The use offlakes of this size has been found to be advantageous in that thecompressive strength of concrete formed using flakes of this size issignificantly enhanced.

The graphene is preferably dispersed or suspended within water prior tothe formation of the concrete material. Preferably, the concentration ofgraphene within the water is in the range of 0.2-2.5 g/L, and morepreferably is in the range of 0.3-1.5 g/L. Preferably, the concentrationis in the range of 0.6-0.8 g/L, and is preferably in the region of 0.7g/L. It has been found that the use of a graphene suspension containinggraphene in these concentrations is advantageous in that the compressivestrength of the concrete formed is significantly enhanced.

The invention further relates to a method of production of concretecomprising the steps of forming a substantially uniform suspension ofgraphene with water, and mixing the suspension with a cementitiousmaterial to form a concrete material.

As set out hereinbefore, the graphene is preferably in the form offlakes. The flakes are preferably of lateral dimensions of less than 5μm, and more preferably have lateral dimensions in the range of 1-3 μm.More preferably, the flakes have a lateral dimension in the range of1.5-2.5 μm, the flakes preferably having a lateral dimension in theregion of 2 μm.

Preferably, the concentration of graphene within the water is in therange of 0.2-2.5 g/L, and more preferably is in the range of 0.3-1.5g/L. Preferably, the concentration is in the range of 0.6-0.8 g/L, andis preferably in the region of 0.7 g/L.

Not only is concrete formed in this manner of enhanced compressivestrength but it also has other enhanced properties. By way of example,its flexural strength is enhanced, and displacement under compressiveloadings is reduced. Its heat capacity is increased, and its waterpermeability is reduced. Additionally, its bond strength to steel mayalso be increased. The material has been found to be suitable for use inthe manufacture of precast concrete products.

As the structural characteristics of the concrete are enhanced,structures manufactured using concrete may require less concrete inorder to be of the required strength. As concrete is not anenvironmentally friendly material, the invention has environmentaladvantages.

The reduced water permeability may increase the range of applications inwhich concrete may be used, for example rendering the material bettersuited to use in applications in areas subjected to flooding.

The suspension of graphene with water may be formed by mixing preformedgraphene flakes with water to form a uniform suspension. Alternatively,graphite powder or graphene powder may be mixed with water and a highshear mixer used to exfoliate the graphite or graphene powder to resultin the formation of graphene suspended within the water. A surfactantsuch as sodium cholate may also be used. The surfactant may serveseveral purposes. Firstly, it reduces the surface tension of the waterto substantially match that of the graphene, making shear exfoliationfeasible. It also aids in the formation of a substantially uniformsuspension of the graphite or graphene powder with the water.Importantly, it also stabilizes the graphene water suspension, reducingaggregation of the graphene.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of steps in a method ofmanufacture of concrete in accordance with an embodiment of theinvention;

FIG. 2 is a graph illustrating the impact upon compressive strength ofconcrete formed with graphene flakes of a range of sizes and in a rangeof suspension concentrations;

FIG. 3 is a graph illustrating the impact upon compressive strength ofconcrete fowled with graphene flakes of a range of sizes and in a rangeof suspension concentrations; and

FIG. 4 is a graph illustrating the impact upon compressive strength ofconcrete formed with graphene flakes of a range of sizes and in a rangeof suspension concentrations.

DESCRIPTION OF THE EMBODIMENT(S)

In describing the embodiment of the present invention, reference will bemade herein to FIGS. 1-4 of the drawings in which like numerals refer tolike features of the invention.

Referring to FIG. 1, steps in a method for use in the manufacture ofgraphene reinforced concrete are illustrated. The method comprises thesteps of adding graphite powder or graphene powder 10, water 12 and asurfactant in the form of sodium cholate 14 to a vessel 16, and using ahigh shear mixing device 18 to mix the graphite or graphene powder 10,water 12 and sodium cholate 14. The presence of the surfactant resultsin the formation of a substantially uniform suspension of the graphiteor graphene powder 10 within the water. The high shear mixing device 18rotates at high speed, for example at a speed in the region of 5000-8000rpm, the mixing device 18 generating sufficiently high shear forceswithin the water 12 that the movement of the water 12 is able to causeexfoliation of the powder 10 to form graphene flakes. By way of example,the graphene flakes may be of few layers form, having ten or fewerlayers. The mixing device 18 is operated for a period of time in theregion of 2 hours to achieve exfoliation of substantially all of thepowder 10. Any relatively heavy remaining powder material 10 may beremoved by decanting the graphene/water suspension. The presence of thesurfactant further serves to result in the graphene forming asubstantially uniform suspension 20 with the water, avoiding significantaggregation of the graphene flakes formed in this manner.

After formation of the graphene/water suspension 20, the suspension 20is mixed with a cementitious material 22 such as Portland cement, sand24 and aggregate or gravel 26 to form concrete 28. The mixing of thesuspension 20 with the cementitious material 22, and 24 and gravel 26 issimilar to the usual concrete manufacturing process with the exceptionthat the suspension 20 is used in substitution for the water that isusually added to the cementitious material, sand and gravel, and therelative proportions of the materials used in the formation of theconcrete is substantially the same as is conventional.

The concrete 28 manufactured in this manner is advantageous compared toconcrete manufactured in the conventional manner in that the compressivestrength and other characteristics thereof are significantly enhanced.By way of example, tests have shown that the compressive strength may beincreased significantly compared to conventional concrete. Furthermore,the flexural strength may be increased significantly, and displacementupon the application of a compressive load may be significantly reduced.The graphene reinforced concrete may have an enhanced heat capacity, andits water permeability may be reduced compared to conventional concrete.The material may have an increased bond strength to steel, and isthought to be suitable for use in the manufacture of precast concreteproducts.

It has been found that the high surface energy of the graphene materialencourages calcium silicate hydrate (C-S-H) particles to bond thereto,forming nucleation sites which promote the growth of the C-S-H gelsalong the graphene flakes. It is the presence of these gels that givesrise to many of the physical characteristics of concrete, and so byproviding the graphene flakes which serve to promote the formation ofthe C-S-H gels, the bond strength of the cement in the concrete isenhanced. Furthermore, the enhanced formation of C-S-H nucleation sitesresults in the formation of a denser network of interlocked cementcrystals which not only gives rise to enhanced physical properties butalso act as a barrier to the ingress of water leading to reduced waterpermeability.

The enhanced physical characteristics have been found to be stable overtime.

The enhanced properties of the graphene reinforced concrete may allowthe quantity of concrete required in certain applications to be reduced,leading to savings and increased efficiencies in those applications. Thereduced amount of concrete, and hence cement, used in such applicationsmay have significant environmental benefits. The reduced waterpermeability may allow the use of concrete in certain applications inwhich, conventionally, concrete would not be suitable for use, forexample in some applications in flood prone areas. Also, the reducedwater permeability may extend the life span of structures exposed towater, in use, without requiring the application of water-resistantadditives or coatings or the like to the structures.

The graphene/water suspension 20 may be manufactured at a high rate, forexample at a rate of 100 L/h or more, and so industrial scale productionof graphene reinforced concrete is possible using the method of thisembodiment of the invention.

As shown in FIGS. 2 and 3, the concentration of graphene within thesuspension is preferably relatively low, for example in the range of 0.2to 2.5 g/L. More preferably, it is in the range of 0.3-1.5 g/L, and itis conveniently in the range of 0.6-0.8 g/L, for example in the regionof 0.7 g/L. The use of a suspension 20 containing this level of graphenehas found to be especially advantageous in that the compressive strengthof concrete manufactured therewith is particularly enhanced.

As shown in FIG. 4, the graphene flakes within the suspension 20 areconveniently of lateral dimensions of less than 5 μm, and morepreferably have lateral dimensions in the range of 1-3 μm. Morepreferably still, the flakes have a lateral dimension in the range of1.5-2.5 μm, the flakes preferably having a lateral dimension in theregion of 2 μm. The use of a suspension 20 including graphene flakes ofthis size is beneficial in that the compressive strength is, again,particularly enhanced.

Although the description hereinbefore is of the use of a surfactantfunctionalized graphene/water suspension in the manufacture of concrete,the invention may alternatively employ graphene produced using othertechniques, and is not restricted to the use of shear exfoliatedgraphene. By way of example, a suspension may be formed by mixingindustrial grade graphene flakes produced using other techniques withwater. Such graphene flakes typically have a slightly greater number oflayers, for example in the region of 10 to 14 layers. Again, asurfactant may be used to avoid aggregation of the graphene flakes, andso assist in the production of a substantially uniform suspension. Thesuspension produced in this manner may then be used in the manufactureof concrete using the techniques outlined hereinbefore.

If desired, the concrete material may further include one or more of arange of additives that are commonly used in the manufacture of concreteto enhance the workability and/or other properties thereof. Theadditives may include, for example, plasticizers or superplasticizers toenhance fluidity and workability, water reducing agents to allow areduced proportion of water to be used in the material, early agestrength improvement agents, retarding admixtures and corrosioninhibiting materials. It will be appreciated that this list is notexhaustive and that other additives may be used, if desired.

The cementitious material 22 may, as mentioned hereinbefore, comprisePortland cement. However, if desired, it may comprise, alternatively oradditionally, a cement replacing material such as ground granulatedblast furnace slag, fly ash, silica fume or limestone fines.

It will he appreciated that the references herein to graphene are notrestricted to monolayer graphene materials but also include other formsof material commonly referred to as graphene, such a bi-layer, tri-layerand few layer graphene, and graphene nano platelets and the like, forexample as defined in ISO/TS 80004-13.

While the present invention has been particularly described, inconjunction with one or more specific embodiments, it is evident thatmany alternatives, modifications and variations will be apparent tothose skilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

Thus, having described the invention, what is claimed is:
 1. Areinforced concrete material comprising a cementitious material in whichgraphene is substantially uniformly distributed.
 2. A material accordingto claim 1, wherein the graphene is in the form of flakes.
 3. A materialaccording to claim 2, wherein the flakes are of lateral dimensions ofless than 5 μm.
 4. A material according to claim 3, wherein the flakesare of lateral dimensions in the range of 1-3 μm.
 5. A materialaccording to claim 4, wherein the flakes are of lateral dimensions inthe range of 1.5-2.5 μm.
 6. A material according to claim 5, wherein theflakes have a lateral dimension in the region of 2 μm.
 7. A materialaccording to claim 1, wherein the graphene is dispersed or suspendedwithin water prior to the formation of the concrete material.
 8. Amaterial according to claim 7, wherein the concentration of graphenewithin the water is in the range of 0.2-2.5 g/L.
 9. A material accordingto claim 8, wherein the concentration of graphene within the water is inthe range of 0.3-1.5 g/L.
 10. A material according to claim 9, whereinthe concentration of graphene within the water is in the range of0.6-0.8 g/L.
 11. A material according to claim 10, wherein theconcentration of graphene within the water is in the region of 0.7 g/L.12. A material according to claim 1, further comprising at least one ofa plasticizer or superplasticizers, a water reducing agent, an early agestrength improvement agent, a retarding admixture and a corrosioninhibiting material.
 13. A material according to claim 1, wherein thecementitious material comprises at least one of Portland cement, groundgranulated blast furnace slag, fly ash, silica fume and limestone fines.14. A method of production of concrete comprising the steps of forming asubstantially uniform suspension of graphene with water, and mixing thesuspension with a cementitious material to form a concrete material. 15.A method according to claim 14, wherein the graphene is in the form offlakes.
 16. A method according to claim 15, wherein the flakes are oflateral dimensions of less than 5 μm.
 17. A method according to claim14, wherein the concentration of graphene within the water is in therange of 0.2-2.5 g/L.
 18. A method according to claim 14, wherein thesuspension of graphene with water is formed by mixing preformed grapheneflakes with water to form a uniform suspension.
 19. A method accordingto claim 14, wherein the suspension is formed by mixing graphite powderor graphene powder with water and using a high shear mixer to exfoliatethe graphite or graphene powder.
 20. A method according to claim 18,wherein a surfactant presents within the suspension.